<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var balance = 100;
        var choice = prompt('请输入您要的操作：\n1.存钱\n2.取钱\n3.显示余额\n4.退出');
        switch (parseInt(choice)) {
            case 1:
                var save = prompt('请输入存入金额');
                balance += parseFloat(save);
                alert('您现在的钱数是：' + balance);
                break;
            case 2:
                var withdraw = prompt('请输入取出金额');
                balance -= parseFloat(withdraw);
                alert('您现在的钱数是：' + balance);
                break;
            case 3:
                alert('您现在的钱数是：' + balance);
                break;
            case 4:
                alert('正在退出');
                break;
            default:
                alert('输入错误');
        }
    </script>
</head>

<body>

</body>

</html>